At present, a fuel battery system which generates power by an electrochemical reaction of a reactive gas (a fuel gas and an oxidizing gas) is proposed and put to practical use. In such a fuel battery system, it is very important to quickly and accurately detect gas leakage in a gas passage for the reactive gas.
For example, in Japanese Patent Application Laid-Open No. 2003-308866, a technology is proposed in which when an electric load of a fuel battery is small, power generation of the fuel battery is stopped, a predetermined closed space is formed in a gas circulation supply system of the fuel battery system, and leakage of the fuel gas is detected based on a pressure state in this closed space.
Moreover, in Japanese Patent Application Laid-Open No. 2004-170321, a technology is proposed in which a pressure on an upstream side of a closed space formed in the gas circulation supply system of the fuel battery system is set to be larger than that of the closed space, a pressure on a downstream side of the space is set to be smaller than that of the closed space, and the leakage of the fuel gas is detected in this state based on a pressure change of the closed space.